api: support delete member by id. (tikv#695)

pd-client: fix a data race in pd client (tikv#660)

Merge pull request tikv#542 from pingcap/tennix/disable-cgo

disable cgo

*: update vendor. (tikv#486)

*: pid to id (tikv#448)

server/cache: hide regions in clusterInfo (tikv#367)

* server/cache: hide regions in clusterInfo

regionsInfo will be rewrote later, we should not access it directly.